1. Field of the Invention
The present invention is directed to a road surface friction coefficient measuring method and device therefor to be utilized in managing the surface of roads on which vehicles such as a car travel or of airport runways.
2. Description of the Related Art
Conventionally, the measurement of the road surface friction coefficient for managing roads and airport runways was ordinarily conducted by running a measuring vehicle comprising a measuring device. For example, with the measuring vehicle 31 shown in FIG. 4 and FIG. 5, a front-wheel-drive vehicle is remodeled and a measuring wheel 33 for measuring the friction coefficient of the road surface G is provided inside the rear trunk room 32. This measuring wheel 33 comprises at the periphery thereof a tire having proximate characteristics of a tire of cars or aircraft that travel on the road surface G, and is mounted on the axle 35 of the travelling wheel 34 via a support arm 36.
The front end of the support arm 36 is rotatably connected to the axle 35 and the rear end thereof supporting the measuring wheel 33 is vertically oscillatable. The measuring wheel 33 contacts the road surface G pursuant to its own weight and the weight of the support arm 36 at the time of measurement. Moreover, rotation of the rear travelling wheel 34 is transmitted to the measuring wheel 33 via a rotation transmission mechanism not shown provided within the support arm 36. Here, when the travelling wheel 34 rotates on the road surface G without slipping due to the difference in the circumferential velocity of the measuring wheel and the circumferential velocity of the travelling wheel, the measuring wheel 33 is structured so as to rotate while slipping on the road surface G at a prescribed slip ratio.
When the measuring wheel 33 travels on the road surface G while slipping, the rotational resistance incurred by the measuring wheel 33 due to the friction with the road surface G is detected by a torque detection means provided within the aforementioned rotation transmission mechanism. A computing device 37 successively calculates the sliding friction of the road surface G to the measuring wheel 33 pursuant to the value detected by the torque detection means described above and the value of the vertical load of the measuring wheel 33 on the road surface incurred by the support arm 36 and its own weight. This calculation result is indicated on the display installed in the measuring vehicle or printed with a printer. Further, a measurement method wherewith a tractional car is equipped with the above-mentioned measurement device has also been conducted heretofore.
Moreover, as another conventional method of measuring the friction coefficient of the road surface, a method is known wherein a tractional measuring vehicle with a pair of wheels mutually facing opposite directions obliquely to the travelling direction is connected to the rear portion of a vehicle to be tracted along the road surface. In this tractional measuring car, the mutually inclined wheels are rotatably mounted respectively to a pair of frames connected in an approachable/separable manner. A load cell is disposed between these frames and this load cell detects the frictional force acting upon the horizontal direction of the respective wheels inclined from the road surface when the tractional measuring car travels on the road surface. The friction coefficient is thereby calculated based on this detected value and the value of the vertical load acting upon the respective wheels from the road surface due to the self weight of the tractional measuring car.
In addition, as another method for measuring the road surface friction coefficient, known is a method of running a vehicle equipped with an accelerometer on the road surface to be measured and measuring the friction coefficient from the deceleration (negative acceleration) upon applying brakes.
With the aforementioned method of measuring the friction coefficient of a road surface utilizing the measuring car shown in FIG. 4 and FIG. 5, the measuring car has a special structure in which a measuring wheel is provided inside the trunk room, and there is a problem in that the costs for remodeling the vehicle body becomes high. Further, upon measuring the friction coefficient of a road surface by tracting a tractional measuring vehicle with a car, it is necessary to make the measuring vehicle heavy to a certain degree such that the wheel can obtain the vertical load from the road surface. As a result, there is a problem in that the size of the measuring vehicle becomes large and the influence of the tractional car becomes great. Moreover, with the tractional car having a pair of wheels arranged obliquely to the travelling direction, there is a problem in that such type of tractional car is inappropriate for measuring snow/ice road surfaces because, in addition to the frictional force acting from the resisting force upon the. wheels oblique to the travelling direction of the measuring vehicle, the resisting force arising from proceeding while scraping the snow and ice is also applied.
Further, with the method of measuring the friction coefficient of a road surface with a car equipped with an accelerometer, there is a problem in that differences arise in the measured values due to the manner of applying the brakes. In addition, it is not possible to use this method for continuous measuring the friction coefficient of airport runways, and there is a problem in that this method can only be used in a limited context.
An object of the present invention i s to resolve the problems of the conventional technology described above, and to provide a road surface friction coefficient measuring method and device therefor which can be used by being easily installed in a general car and is capable of measuring the friction coefficient of various road surfaces, such as roads and runways, at a high degree of accuracy.
A road surface friction coefficient measuring method according to the present invention for achieving the aforementioned object comprises the steps of: providing a measuring wheel on the outside of the travelling wheel of a car via a support arm provided oscillatably about the axis line of the travelling wheel; generating frictional force of the ground surface to the measuring wheel by rotatably driving the measuring wheel so as to have a prescribed difference in circumferential velocity from the travelling wheel; applyingg a vertical load to be added to the self weight of the measuring wheel by applying a prescribed vertical load to the measuring wheel; and measuring the frictional force and the vertical load and calculating the road surface friction coefficient based on the measured values.
And a road surface. friction measuring device according to the present invention for achieving the aforementioned road surface friction coefficient measuring method comprises: a spindle connected and secured to the outside of a travelling wheel of a car on the axis line to the axle; a support arm in which one end thereof is rotatably connected about the axis line of the spindle and the other end thereof is supporting the axle of measuring wheel; a measuring wheel rotatably supported about the axis line parallel to the spindle at a position apart from the spindle at the other end of the support arm; a rotation transmission mechanism for transmitting to the measuring wheel the rotation of the spindle so as to provide a prescribed circumferential velocity difference between the travelling wheel and measuring wheel; a vertical load generating mechanism for applying a vertical load to be added to the self weight of the measuring wheel; first detection means for detecting the vertical load; second detection means for detecting the frictional force upon the measuring wheel slipping and rotating on the road surface; and computing means for calculating the slip friction coefficient to the road surface and measuring wheel based on the detected values respectively obtained from the first detection means and second detection means and the self weight of the measuring wheel including the arm.
By mounting the spindle detachably on the wheel of the travelling wheel, the device can be easily installed in a general car. Employed as the rotation transmission mechanism may be one among a gear train transmission mechanism, chain transmission mechanism, bevel gear transmission mechanism, or belt transmission mechanism. The vertical load generating mechanism may , for example, comprise a disk brake mechanism in which a brake disk is secured to the spindle side and a caliper is provided on the support arm side, apply braking force to the travelling wheel from the support arm, and generate a vertical load to be added to the self weight of the measuring wheel as a reactive force. In addition, adequately employed as a vertical load generating mechanism may be a structure in which a power generator is provided to the support arm side and which obtains braking force by power generation upon rotating the power generator with the spindle, or a structure having a counter weel.